Формула Crystal Report для расчета баланса по кредиту и дебету

hi,


In my web Application i have showing report for "Customer Ledger"

Here i need to display report as follows...

BillNo|Credit | Debit  | Balance
--------------------------------------
B0982 | 1000  |    0   |   -1000
B0999 | 2000  |    0   |   -3000
B0982 |  0    |  2200  |   -800
B1200 | 5000  |    0   |   -5800


Likewise i need to Calculate my <b>"BALANCE".</b>

I have populate credit and debit from the DB, but now i need to Calculate Balance alone.

I have <b>"TotalAccountAmount"</b> which describe the total <b>amount of Billing</b> made for a particular customer. Now i need to calculate these above scenario based on my "TotalAccountAmount"

Please help me how to do it with CrystalReport FormulaField ???